/**
 * 接口客户端。
 *
 * 三条约定：
 * 1. 后端永远返回 {code,message,data,request_id}，code !== 0 一律抛出。
 * 2. 写请求自动带 Idempotency-Key，网络抖动重试不会重复建数据。
 * 3. 401 统一清理本地令牌并回到登录页，不在业务里各写一遍。
 */

const BASE = "/api/v1";

export class ApiError extends Error {
  constructor(
    readonly code: number,
    message: string,
    readonly requestId?: string,
  ) {
    super(message);
    this.name = "ApiError";
  }
}

export interface Tokens {
  access_token: string;
  refresh_token: string;
  expires_in: number;
}

const ACCESS_KEY = "dadao.access";
const REFRESH_KEY = "dadao.refresh";

export const session = {
  get access(): string | null {
    return localStorage.getItem(ACCESS_KEY);
  },
  get refresh(): string | null {
    return localStorage.getItem(REFRESH_KEY);
  },
  save(tokens: Tokens) {
    localStorage.setItem(ACCESS_KEY, tokens.access_token);
    localStorage.setItem(REFRESH_KEY, tokens.refresh_token);
  },
  clear() {
    localStorage.removeItem(ACCESS_KEY);
    localStorage.removeItem(REFRESH_KEY);
  },
};

export const authExpired = new EventTarget();

/**
 * 幂等键。
 *
 * 别直接用 `crypto.randomUUID()`：它只在**安全上下文**（https 或 localhost）里存在，
 * 而内网生产入口是纯 http，那里 `crypto.randomUUID` 是 undefined，调它会把
 * 所有写请求变成 "登录失败" 这种莫名其妙的报错——GET 没事，所以特别难发现。
 * `getRandomValues` 不受这个限制，退回它自己拼一个 v4。
 */
function newIdempotencyKey(): string {
  const c = globalThis.crypto;
  if (typeof c?.randomUUID === "function") return c.randomUUID();
  const bytes = new Uint8Array(16);
  if (typeof c?.getRandomValues === "function") {
    c.getRandomValues(bytes);
  } else {
    for (let i = 0; i < bytes.length; i += 1) bytes[i] = Math.floor(Math.random() * 256);
  }
  bytes[6] = (bytes[6] & 0x0f) | 0x40;
  bytes[8] = (bytes[8] & 0x3f) | 0x80;
  const hex = Array.from(bytes, (b) => b.toString(16).padStart(2, "0")).join("");
  return `${hex.slice(0, 8)}-${hex.slice(8, 12)}-${hex.slice(12, 16)}-${hex.slice(16, 20)}-${hex.slice(20)}`;
}

type Method = "GET" | "POST" | "PATCH" | "PUT" | "DELETE";

interface RequestOptions {
  method?: Method;
  body?: unknown;
  signal?: AbortSignal;
  /** 幂等键；不传则对写请求自动生成 */
  idempotencyKey?: string;
}

async function raw<T>(path: string, opts: RequestOptions = {}): Promise<T> {
  const method: Method = opts.method ?? "GET";
  const headers: Record<string, string> = { Accept: "application/json" };
  if (opts.body !== undefined) headers["Content-Type"] = "application/json";

  const token = session.access;
  if (token) headers.Authorization = `Bearer ${token}`;

  const isWrite = method !== "GET";
  if (isWrite) {
    headers["Idempotency-Key"] = opts.idempotencyKey ?? newIdempotencyKey();
  }

  const resp = await fetch(`${BASE}${path}`, {
    method,
    headers,
    signal: opts.signal,
    body: opts.body === undefined ? undefined : JSON.stringify(opts.body),
  });

  let body: { code: number; message: string; data: T; request_id: string } | null = null;
  try {
    body = await resp.json();
  } catch {
    body = null;
  }

  if (!body) {
    throw new ApiError(resp.status, `服务返回了非 JSON 响应（HTTP ${resp.status}）`);
  }
  if (!resp.ok || body.code !== 0) {
    if (resp.status === 401) {
      session.clear();
      authExpired.dispatchEvent(new Event("expired"));
    }
    throw new ApiError(body.code, body.message, body.request_id);
  }
  return body.data;
}

export const api = {
  get: <T>(path: string, signal?: AbortSignal) => raw<T>(path, { signal }),
  post: <T>(path: string, body?: unknown) => raw<T>(path, { method: "POST", body }),
  patch: <T>(path: string, body?: unknown) => raw<T>(path, { method: "PATCH", body }),
  del: <T>(path: string) => raw<T>(path, { method: "DELETE" }),
};

/**
 * 上传文件（multipart）。
 *
 * 不能用 api.post：它固定发 JSON。这里也不能自己设 Content-Type，
 * 必须让浏览器带 boundary，否则 FastAPI 解析不出文件。
 */
export async function uploadFile<T>(path: string, file: File): Promise<T> {
  const form = new FormData();
  form.append("file", file, file.name);

  const headers: Record<string, string> = { Accept: "application/json" };
  const token = session.access;
  if (token) headers.Authorization = `Bearer ${token}`;
  headers["Idempotency-Key"] = newIdempotencyKey();

  const resp = await fetch(`${BASE}${path}`, { method: "POST", headers, body: form });

  let body: { code: number; message: string; data: T; request_id: string } | null = null;
  try {
    body = await resp.json();
  } catch {
    body = null;
  }
  if (!body) {
    throw new ApiError(resp.status, `上传失败：服务返回了非 JSON 响应（HTTP ${resp.status}）`);
  }
  if (!resp.ok || body.code !== 0) {
    if (resp.status === 401) {
      session.clear();
      authExpired.dispatchEvent(new Event("expired"));
    }
    throw new ApiError(body.code, body.message, body.request_id);
  }
  return body.data;
}

/**
 * 附件直链：`<img>` 带不了 Authorization 头，所以令牌走 query。
 * 只在渲染 Markdown 图片时用，不要拿它去做普通的下载链接（那样 token 会留在浏览器历史里）。
 */
/** 入库用的规范地址：不带任何查询串，抬头签名由渲染层按附件列表现配。 */
export function canonicalAttachmentPath(wsId: string, attachmentId: string): string {
  return `${BASE}/workspaces/${wsId}/attachments/${attachmentId}/raw`;
}